Field
This invention pertains to the cathodic protection of metallic structures such as drilling rigs, sea walls and the like disposed in contact with marine environments. It is specifically directed to systems including sacrificial anodes disposed within the marine environment and electrically coupled to the structure being protected. It provides a new assembly of components whereby the surface area of sacrificial anode material exposed to the sea water environment may be adjusted as needed to control the current density of the circuit between the anode material and the structure.
State of the Art
The cathodic protection of off-shore platforms and drilling ships, bridges and other structures exposed to marine environments is an art which has been practiced for many years. The objective of all such systems is to adjust current flow from anodes to the structure thereby to elevate the polarization level of the structure within the "protected" range; that is, the level at which electron emission from the protected structure to the marine brine is substantially inhibited, thereby suppressing corrosion of the structure.
Among the systems employed in the past have been the so-called "impressed current" systems whereby a power supply is used to impress a potential difference between the structure and an anode suspended in the sea water environment. These systems are sometimes automated to adjust the current flow by adjusting the driving voltage through a power supply connected to the anodes. Other systems have involved magnesium anodes coupled to the structure and including an adjustable resistance between the anode and ground to control the current flow through the circuit. These resistances result in a very low coulomb efficiency. Moreover, none of the prior art systems are adequately responsive to changing environmental conditions. Further, the maintenance and installation costs of the prior art systems have been unacceptably high.